Author Topic: New (to me) Lathe - Smart & Brown 1024  (Read 1470 times)

Offline Charles

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New (to me) Lathe - Smart & Brown 1024
« on: June 19, 2017, 05:29:56 PM »
I started out in the world of machine tools with a Myford Super 7, lovely machine, but I soon realised it wasn't man enough for what I wanted to do, so I started looking around for an old, preferably English toolroom lathe. Almost by accident, I acquired a smart and Brown Model A, which is fantastic - a far better lathe than I am a machinist... But I've kinda been hankering after its big brother so when one appeared on the Yahoo group for a very acceptable price I couldn't really say no...

The good news is it was cheap, local and almost complete... The not so good news is it's in bits, there's no toolpost, it was taken out of use in its former life because the power feed wouldn't engage/disengage reliably, and its 3 phase.

So, the to-do list:
Rebuild the apron, fixing the power feed problem on the way,
re-make the cover for the apron (unless it turns up in the meantime)
clean it
repair / rebuild the coolant tray which has rusted through
strip the wiring out and make it run from an inverter
find a toolpost
put it all back together

I found a small single phase pump in a skip the other day which looks like it might do duty for the coolant, so that's one job ticked off already! the rest will have to wait a few weeks as the dairy is pretty full...

In the meantime, some questions...
can anyone identify the mystery tool holder? could be yours if you can use it...
The lathe came with some tool holder's, I believe they fit a T2 QCTP, they are stamped Colchester. does anyone has a toolpost to fit that they could be parted from, or would they like to acquire them?
Does anyone in the Hampshire area own one of these beauties, it would be really helpful to have a look at the power feed mechanism, apparently there is a spring missing from mine, I have the drawings, but there's no substitute for seeing it in the flesh...

Offline hopefuldave

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #1 on: June 21, 2017, 06:28:32 PM »
Hello Charles,

How may of the toolholders do you have? a size 2 (I think) Dickson but only two holders came with my Holbrook and I'd be keen to get a few more - where in Hampshire are you (I'm near M3 Junction 3), if you want a hand with the VFD conversion I've had a bit of practice!

Dave H. (the other one)
Rules are for the obedience of fools, and the guidance of wise men.

Offline Charles

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #2 on: June 22, 2017, 06:39:55 AM »
Dave,

I have three tool holders, I'll wave a tape measure at them tomorrow and you can check against your tool post. I'm in Eastleigh - J13 M3 I set up the VFD on my milling machine, so have had a bit of practice, but I will let you know if I get stuck. I believe the 1024 has a 3 speed motor which makes things a little more challenging

Offline RotarySMP

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #3 on: June 22, 2017, 03:18:48 PM »
really nice lathe you have there.

Offline Charles

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #4 on: June 23, 2017, 04:53:39 PM »
Toolholders certainly look like T2 size, There are three of them. as you can see they are missing a couple of screws, but that should be no big deal for your Holbrook to rectify :ddb:

Looks like new ones are about 35, so how does 20 each sound? Assuming they would be of use to you...

How did you find your Holbrook? that was one for my shortlist when I decided to upgrade the Myford, but they seem to be pretty rare...

RotarySMP - I hope so!

Offline hopefuldave

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #5 on: June 24, 2017, 07:19:59 AM »
Thanks Charles, I'll have to check the wallet... A few other projects going on at the mo', bought a Substantial oldish milling machine a few weeks ago and I'm mid-way through buying bits for and building a 240-415 rotary convertor to power it - the Holbrook's fitted with a VFD hacked to give 415 from 240 in, simple mod' on an older VFD (ABB ACS-300 series) but I ran into the same issue with a 3-speed motor, I *think* the work-around is successful (so far) though!

When converting your Harrison, something to ensure is that the VFD output's disabled in some way if/while switching motor windings - the Holbrook has a microswitch on the speed-change lever (originally dropped out a main contactor) that I've used to a) disconnect the fwd/reverse switch's common feed and b) switch between stop/start configurations so it goes into "freewheel and brake" / "boost" stop / start mode with a longer freewheel interval (1 second, to allow time to move the lever!) by toggling the "parameter set 1/2" input, plus I've added a trio of homebrew load reactors between VFD and speed-change switching (the "Frankenstein Switch") and 1kV MOV over-voltage devices across the motor windings to limit inductive spikes - I simulated it all in LabView and got the results I was looking for, works (so far...).

Some more modern VFDs have a "gate block" input that effectively isolates their outputs (putting the motor in freewheel), may do the necessary but I'd still be wary of inductive spikes from switching windings, and the "gate block" would need to operate before the speed-change switch (the Holbrook has a "gate" on the speed-change lever, moving out of the detents operates the microswitch).

I found the Holbrook (model C13 from about 1955) on EvilBay a few years ago to replace my previous Challenger AG, it's been a bit of a labour of love! ALL the existing control gear had to come out (would have done it anyway as the relays had 415v coils, so 415 to all the switchgear - ouch!) and I'm still looking for a few parts for it and making some others - it cost me a lot less than a secondhand mini-lathe at the time, though, probably because it's not a "name" machine to many and it looked, frankly, Horrible* - it cleaned up a treat, but in the process I discovered a  few things (mostly made of Unobtainium) needing attention or making :)

Once the new old mill's up and running I have a Cunning Plan (thanks Baldrick) to add a fourth control shaft and gubbins for feed/leadscrew reverse, something the Holbrook Model T and H have but which was missed out on the Model C, inexplicably, although the space and most of the necessary parts are there anyway! A helpful lad at work is going to 3D print transparent plastic mock-ups so I can see where I've gone wrong before I start casting and machining parts... Lending him a few hand tools to modify his Airsoft armoury and giving Clear Instructions has worked out well :)

Dave H. (the other one)

* Painted with either an old carpet or a dead dog, compacted swarf and coolant hiding sound metal...
Rules are for the obedience of fools, and the guidance of wise men.

Offline Charles

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #6 on: June 26, 2017, 04:54:51 PM »
Thanks for the info, a couple of questions; possibly silly ones as motor theory has never been one of my strong subjects...

Since the VFD gives infinite speed control, what is the advantage of using the original multi-speed motor windings? in other words why not connect directly to the fastest winding and let the VFD handle the slower speeds? And, if your VFD has been hacked to give 415v out, does this mean that the motor is wired star? if so, what is the motors neutral/centre of star connected to?

There's an ABB ACS-300 on eBay at the moment for $600  :bugeye: don't think I'll be using one of those when the generic Chinese ones can be had for 80!

I would be interested to know a little more about you RPC, cost/complexity etc, as this would allow the use of the original switchgear and potentially save a major rewiring exercise.

Offline Bluechip

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #7 on: June 26, 2017, 05:27:42 PM »
3-Ph. star connected motors don't use a neutral.

The star point is not generally brought out as such. It's just the ends of the three windings that get connected together.

Pic. gives the general idea,  just swiped off the net.

Delta = Mesh, Star = Wye. Different names for the same thing.

D.
« Last Edit: June 26, 2017, 05:54:49 PM by Bluechip »
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Offline Charles

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #8 on: June 27, 2017, 07:35:33 AM »
Bluechip - thanks that makes sense, i guess a motor is inherently a balanced load, so doesn't need a neutral..

Offline hermetic

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #9 on: June 28, 2017, 02:50:52 PM »
You need to remember that if you slow the motor down too much, the cooling will be comprimised and you may need to put an  extra cooling fan to blow on the motor. VFD's can damage windings at high frequencies especially if the windings are not encapsulated in resin, if they are, no problem. Far better to use a 240v to 415 volt inverter, and change speeds with the gearbox!
Phil

Offline hopefuldave

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #10 on: June 29, 2017, 07:29:18 PM »
Evening Charles, apologies for the delay - had a few late nights at work :(

I kept the three-speed switch as I wanted to have best-possible torque at low speeds (and the full Holbrook Experience) - the 4-6-8 pole motor gives more torque and usable power (twice as much, at least) in the low-speed (8pole) config' than running the VFD at a low frequency (although I can and do run down as low as 5Hz/2.2 spindle RPM for "jog" and a few special applications), its inductance in 8-pole chokes off the winding current at high frequencies (I go as high as 83 Hz to get the spindle up to 2500 RPM for short periods rather than the original 1500 max.). The Holbrook also has a bit of an inconveniently big gap between the two top speeds, a VFD allows a bit of fine-tuning and some clever stuff like near-constant surface speed for facing and parting (like the Big Boys have on their CNC machines), dynamic braking etc.
I use a configurable relay in the VFD to switch *off* an external fan mounted on the end of the motor when the VFD output gets *above* 30Hz to ensure it gets enough cooling airflow (and it cools it between runs - plus it reminds me I've left the power on!)

As for star points... the Holbrook's motor uses a Dahlander pole-switching setup for the 4 and 8 pole settings (which switches power to the middle of each phase winding of what would otherwise be a delta-winding and connects the "corners" into a "star" point versus just powering the corners) and a separate delta winding for 6-pole use - which is probably why its motor's getting on for the size of a dustbin while only making 3 HP! It takes some thought to get your head around (or mine, at least...)

The RPC is currently coming together (slowly, waiting on the proverbial Slow Boat from...), built on a budget:

5.5 KW (7.5HP) 3-phase 415v 4-pole motor off EvilBay for 70;
Oxford 180A oil-cooled welder (ancient, 240 and 415 tapped primary, 6.5 KVA *continuous* rating, peak 11 KVA - should do the job!) 19 off EvilBay;
32A type-C MCB for 240v input, assorted contactors, 9-13A motor overload (plugs into motor contactor),16A 3-phase MCB, 40A 3-phase RCD (EvilBay) between 5 and 15 each;
Handful of "RUN" rated capacitors for the motor start circuit (50, 100, 200, 300 uF 460 acv - to mix and match) 5-8 each on EvilBay;
3 off on/off/lamp pushbuttons 1.99 each on EvilBay;
24v control transformer (for contactors and lamps) from my junk pile;
pair of 16A 3-phase sockets (junk pile);
small electrical cabinet with the door cut out and replaced with some Alupanel to take meters, sockets, switches etc., 2.5mm/4mm SY braid-covered cabling to hook bits up, all skip-dived at work :);
lily-gilding: 3 off 500vac meters for phase-to-phase; 3 off 20Aac meters for the phases and a 50Aac meter for the input, 5 - 8 each, guess where; 24v panel lamps for fault indication 1.29 each....

Soooo - a couple of hundred quid, with careful shopping?

The motor and transformer are both a little bigger than I was expecting so they'll be living outside in a kennel built from some leftover Dexion shelves and angle!

The RPC is probably needlessly complicated, but not a patch on the VFD implementation on the lathe...

Dave H. (the other one)
(previously an electrical / electronics engineer by trade, in case you hadn't guessed, now moved on to photons, bits and picoseconds)
Rules are for the obedience of fools, and the guidance of wise men.

Offline hopefuldave

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #11 on: June 29, 2017, 07:38:08 PM »
Not the final wiring diagram, I keep revising it, but a starting point:

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Offline Charles

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Re: New (to me) Lathe - Smart & Brown 1024
« Reply #12 on: July 04, 2017, 08:17:07 AM »
Wow,

thanks very much for the detailed post :nrocks:

I presume that the S&B motor is the same configuration as the Holbrook one, I wasn't aware that the lower speeds would give better torque, but it makes sense. I would say that's a very good reason to go to the trouble you describe!

I shall have to investigate the condition of the wiring and switch gear before I make a decision on which way to go with this...